So before we begin discussing in detail how bone is made, let's look at the overall classification as well as the function that bones serve. So bones are classified into two major groups based on their location. The axial skeleton, which we will cover, in module 7 is along the long axis of the body and this is going to include the skull the vertebral column and the ribcage in module 8 we are going to cover the appendicular skeleton so the appendicular skeleton includes all the bones of your limbs both upper limbs it's like your arms and hands and your lower limbs your legs and feet So there are particular girdles that help to attach these limbs to the axial skeleton. So think of the pelvis, for example, as a girdle. Overall, there's about 206 named bones in the skeleton.
So that's if we classify bones based on location. We could also classify bones based on shape, and there are five major shapes. Number one...
are the long bones. And they're called long bones because they are longer than they are wider. So a classic example would be the humerus here, but it does include the limb, the wrist, as well as the ankle bones.
Then you have the short bones. The short bones tend to be cube-shaped, and some of the bones within the wrist and within the ankle fall under this purview. Within short bones, and some textbooks will place sesamoid bones within short bones, other textbooks will place them into their own separate little category that I have over here, but basically sesamoid bones are short bones but they're embedded within tendons.
So these short bones can vary in size from one person to another. to the next. So in this particular figure, we have an example of a short bone here, the talus.
So it's part of your ankle. Number three are the flat bones. And just because the name is flat, has flat, it doesn't mean it's literally flat.
Oftentimes these bones are relatively thin and they might have curves. So think of the... bones of the skull as a flat bone.
Another flat bone would be, as shown here, the breast bone or the sternum. And our fourth category are irregular bones because they have very complicated shapes. They don't fit in the other three categories.
So among these are the coxal bones, which make up the pelvis and the various vertebrae. So what are the functions of bones? Well, bones have a lot of function.
It's not just for support. It's not just a scaffold on which other things depend. So number one, yes it is for support for your body and organs.
It's there to protect various structures like the brain, the spinal cord, and the internal organs. In conjunction with muscle action, It functions in movement. So muscles are attached to bones, and when muscles contract, the muscles work sort of like a lever system to generate that movement. Number four, bones serve as a repository for very crucial minerals like calcium and phosphorus, as well as for growth factors. In fact, 99% of the calcium in your body...
is locked into bones. Number five, blood cell formation. So specifically within bones, not all of them, but at the tips of the long bones, you have what is called red bone marrow. And housed within this red bone marrow, you have stem cells that are very important for hematopoiesis. That is the process of forming the various blood cells.
So those include red blood cells, white blood cells, and platelets needed for clotting. Number six, you have fat storage. So there's a different type of marrow here called yellow marrow. This is what you usually find in the shafts of the long bones. Lots of energy storage.
So if you've ever made any kind of bone broth, you leach the fat out of the bone and the cocktail that you make actually will congeal if you let it cool down. This is also why your dog likes to chew on bones to access that fat. Number seven, bones are very important for certain hormones and their production. So a particular hormone that's very important is osteocalcin. It helps to regulate bone formation, but it also has rules in protecting against obesity, glucose intolerance, as well as diabetes.